The infant's world is filled with objects; objects with unknown names. But learning the names for these objects - mapping auditory word forms onto objects in visual scenes - requires young learners to contend with significant uncertainty. When the infant's caretaker produces a word, the child must determine to which object, if any, it refers The solution is straightforward for adults and for older children: they consult the social cues produced by the speaker (e.g. pointing, gaze) to determine the target object. However, the way that infants solve this referential uncertainty problem, and the way that they learn to use social cues to reference, remains the topic of significant debate. The proposed project will produce insight into both of these questions through three integrated lines of research. Because competing theories about the origins and development of the use of social cues have used very different experimental methodology, their results have proven to be difficult to integrate. Thus, Specific Aim 1 is to measure infants' use of cues to reference, in a single paradigm, over a broad range of early development. Experiments 1 and 2 use eye-tracking methods to measure how infants learn words from different cues to reference (salience, eye-gaze, pointing, and action), both alone and together, from 9-months to 24-months. This data will let us determine both the ages at which infants begin to use these cues, and also the trajectories they follow to become mature users of social cues. Second, we will use head-mounted cameras to record natural naming events to children, collecting data about the events from which infants could learn about social cues to reference. These data will allow us to determine the extent to which trajectories of cue use can be explained by their presence and predictive validity in children's language input. In conjunction with this data, we will use a set of computational models to address Specific Aim 2: to understand how children learn to use social cues to learn language from social partners. These three integrated approaches will advance our understanding of the basic learning mechanisms used by young children in order to learn language. Together, they will also inform the construction of tools for assessment and diagnosis of language learning in young children. Further, modeling the normative mechanisms by which children learn to use social information for language learning can point to potential interventions for children with difficulties in this aspect of language acquisition. This is likely to be of particular relevance t children with autism spectrum disorder.